Remember with /click it actually clicks on all of the Action Buttons at the same time.

Under my last button I have:
#show Incincerate (so i dont have to find the damn icon)
/use 13
/use 14
/cast [pet:imp] fireball
/cast Incinerate

My Imp will always cast at my target even if I change targets - having him cast all the time has increased my DPS dramatically. I've been doing 4-6k DPS quite easily and my Warlock is in pretty shitty gear compared to my Shaman. They seem to cap out at about 5.5k tops with the occasional string of luckky crits getting me to 6k.

4k is pretty average though and what I'm used to seeing unless its a boss fight. 2k if the mobs have very little health.